Summary Tables
For Sizing Calculations For Air Conditioning And Refrigeration Equipment As Per
NEC Article 440

First:
Sizing Calculations for Disconnecting Means

Summary
Of Sizing Steps For Disconnecting Means For
Single
Hermetic Motor Only


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Step#1

Select AR of disconnecting
means ≥ 115% of the compressors rated load current or branchcircuit
selection current, whichever is greater.

Step#2

Calculate the
greater value A or B of equivalent horsepower rating for the selected disconnecting means
in Step#1.

A

Use NEC
Tables 430.248, 430.249 or 430.250 using the greater of either the rated load
current or the branch circuit selection current.

B

Use NEC
Tables 430.251(A) and 430.251(B) using the lockedrotor current.

Step#3

The Selected
disconnecting means from step#1 must have HP rating ≥ the equivalent
horsepower rating from step#2. If not, repeat step#1 with higher value of AR.

Notes:

Summary
Of Sizing Steps For Disconnecting Means For
Combination
loads


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Step#1

Select AR of disconnecting
means ≥ 115% of the sum of all of the individual loads at rated load
conditions.

Step#2

Calculate the
greater value A or B of equivalent horsepower rating for the selected disconnecting means
in Step#1.

A

Use NEC
Tables 430.248, 430.249 or 430.250 using the sum of all of the individual
loads at rated load conditions, where:
The sum of
all of the individual loads at rated load conditions = motorcompressor
ratedload current(s) or branchcircuit selection current(s), whichever is
greater + fan /blower motors ratedload current(s) + full load currents of
other motors + the rating in amperes of other loads

B

Use NEC
Tables 430.251(A) and 430.251(B) using the sum of all of the individual loads
lockedrotor currents, where:
The sum of
all of the individual loads lockedrotor currents = motorcompressor
lockedrotor current + fan /blower motors lockedrotor current(s) +
lockedrotor currents of other motors + the rating in amperes of other loads.

Step#3

The Selected
disconnecting means from step#1 must have HP rating ≥ the equivalent
horsepower rating from step#2. If not, repeat step#1 with higher value of AR.

Notes:

Second:
Sizing calculation for BranchCircuit ShortCircuit and GroundFault
Protection Devices

Summary
Of Sizing Steps For BranchCircuit
ShortCircuit and GroundFault Protection Devices For Single Hermetic Motor Only


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Step#1

Size the short circuit and
ground fault OCPD AR ≤ 175% of the motorcompressor ratedload current or branchcircuit
selection current, which‐ ever is greater.

Step#2

Compare the time current curves for both the
motor and the circuit breaker:
If there is intersection, go to step#3,
If not, the OCPD
AR is adequate (end of sizing calculations).

Step#3

Size the short circuit and
ground fault OCPD AR ≤ 225% of the motorcompressor ratedload current or branchcircuit
selection current, which‐ ever is greater.

Notes:

Summary
Of Sizing Steps For BranchCircuit
ShortCircuit and GroundFault Protection Devices For Combination Loads


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Case# A: Where a hermetic refrigerant
motorcompressor is the largest load


Step#1

OPCD AR = 175% of the largest motorcompressor ratedload current or branchcircuit selection current, which‐ ever is greater + the sum of the ratedload current or branchcircuit selection current, whichever is greater, of the other motor compressor(s) + the ratings of the other loads. 
Step#2

Compare the time current curves for both the
motor and the circuit breaker:
If there is intersection, go to step#3,
If not, the OCPD AR is
adequate (end of sizing calculations).

Step#3

the Maximum OverCurrent
Protection (MOP) = 225% of the largest
motorcompressor ratedload current or branchcircuit selection current,
which‐ ever is greater + the sum of the ratedload current or branchcircuit
selection current, whichever is greater, of the other motor
compressor(s) + the ratings of the other loads.

Case# B: Where a hermetic
refrigerant motorcompressor is not the largest


Step#1

OPCD AR = the ratedload current or branch circuit selection current,
whichever is greater, rating(s) for the motorcompressor(s) + the ratedload
current For other motor loads not exceeding 800A + the ratedload current for
other loads

Step#2

Compare the time current curves for both the
motor and the circuit breaker:
If there is intersection, go to step#3,
If not, the OCPD AR is
adequate (end of sizing calculations).

Step#3

the Maximum OverCurrent
Protection (MOP) = 225% of the largest Load rated current or branchcircuit selection
current , whichever
is greater + the sum of the ratedload
current or branchcircuit selection current, whichever is greater, of the
motor compressor(s) + the ratings of the other loads.

Notes:

Third:
Sizing Branch Circuit Conductors

Summary
Of Sizing Steps For BranchCircuit Conductors
For
Single Hermetic Motor Only


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Step#1

If the equipment is marked with minimum circuit ampacity
(MCA), use this value to size the branch circuit
conductors. If not, go to Step#2.

Step#2

Size the branch circuit
conductors ampacity ≥ 125% of the motor compressor
ratedload current or the branch circuit selection current, whichever is
greater

Special Case

For a WyeStart, DeltaRun Connected
MotorCompressor:
The branchcircuit conductors
ampacity between the controller and the motorcompressor = 72 % of either the
motorcompressor ratedload current or the branchcircuit selection current,
whichever is greater.

Notes:

Summary
Of Sizing Steps For BranchCircuit Conductors
For
Combination Loads


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Step#1

If the
equipment is marked with minimum circuit ampacity (MCA), use this value to size the branch circuit conductors. If not, go
to Step#2.

Step#2

Size
Branch circuit conductor ampacity = 125% of the largest motorcompressor
ratedload current or branchcircuit selection current, which‐ ever is
greater + the sum of the ratedload current of the other motor + the ratings
of the other loads.

Notes:

Fourth:
Sizing Controllers

Summary
Of Sizing Steps For Controller Serving Motor Compressor
only


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Step#1

The
controller must have a continuous duty FLC ≥ the nameplate rated current or
branch circuit selection current (whichever is larger),

Step#2

And also,
The controller must
have a LRC ≥ the locked rotor current of the compressor .

Notes:

Summary
Of Sizing Steps For Controller Serving More Than One Load


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Step#1

The ampere rating of the Controller ≥ 115% of the sum of all
of the individual loads at rated load conditions

Step#2

Calculate the
greater value A or B of equivalent horsepower rating for the selected disconnecting means
in Step#1.

A

Use NEC
Tables 430.248, 430.249 or 430.250 using the sum of all of the individual
loads at rated load conditions, where:
The sum of
all of the individual loads at rated load conditions = motorcompressor
ratedload current(s) or branchcircuit selection current(s), whichever is
greater + fan /blower motors ratedload current(s) + full load currents of
other motors + the rating in amperes of other loads

B

Use NEC
Tables 430.251(A) and 430.251(B) using the sum of all of the individual loads
lockedrotor currents, where:
The sum of
all of the individual loads lockedrotor currents = motorcompressor
lockedrotor current + fan /blower motors lockedrotor current(s) +
lockedrotor currents of other motors + the rating in amperes of other loads.

Step#3

Select Controller
with HP rating ≥ the equivalent horsepower rating from step#1. If not, repeat
step#1 with higher value of AR.

Notes:

Fifth:
Branch Circuit Overload Protection

Summary
Of Sizing Steps for Branch Circuit
Overload Protection
for Air Conditioning and Refrigeration Equipment


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Option#1

When using A
separate overload relay, The relay must be selected to trip at no more than
140% of the motorcompressor ratedload current.

Option#2

When
using a Thermal Protector, it must not permit a continuous current in excess
of 156 percent of the marked ratedload current or branchcircuit selection
current.

Option#3

When using A
fuse or inverse time circuit breaker, The device must be rated for no more
than 125% of the motor compressor rated load current.

Option#4

When
the manufacturer uses a special protective system, it must not
permit a continuous current in excess of 156 percent of the marked ratedload
current or branch circuit selection current.

Notes:

Sixth: Provisions for Room Air Conditioners 
Summary of
Sizing Steps for Provisions for Room Air Conditioners


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Sizing
BranchCircuit ShortCircuit and GroundFault Protection

Equipment that starts
and operates on a 15 or 20 ampere 120volt, or 15ampere 208 or 240volt
singlephase branch circuit, shall be permitted to be protected by the 15 or
20ampere over‐ current device protecting the branch circuit, [440.22(B) exception#1].
The nameplate marking
of cordandplugconnected equipment rated not greater than 250 volts,
singlephase, such as household refrigerators and freezers, drinking water
coolers, and beverage dispensers, shall be used in determining the branch
circuit requirements, and each unit shall be considered as a single motor
unless the nameplate is marked otherwise [440.22(B) exception#2].

Sizing Branch
Circuit Conductors

If
a room air conditioner is the only load on the circuit, the circuit must be
rated for 125% of the marked rating of the air conditioner.
If
the room air conditioner is to be supplied from a standard receptacle circuit
and other loads may be supplied from the circuit, the branch circuit must be
rated at least 200% of the air conditioners marked rating.

Sizing
Disconnecting Means

an
attachment plug and receptacle can be used as the sole disconnecting means as
long as one of two conditions is met:
The
manual controls for the AC unit are readily accessible and located no more
than 1.8 m (6 feet) of the floor.
An
approved manually operable switch is installed in a readily accessible
location that is in sight of the AC unit.

Protection
Device For the Cord

As
per NEC 440.65, the manufacturer must install one of the following protection
devices:
The protection device shall be an integral part of the attachment plug or be
located in the power supply cord within 300 mm (12 in.) of the attachment
plug.

Notes:

In
the next article, we will solve some examples for sizing calculations of Air
Conditioning and Refrigeration Equipment as Per NEC Article 440. So,
please keep following.
The previous and related articles
are listed in below table:
Subject Of Previous
Article

Article

Summary of
heating and cooling systems,
Parts Consuming
Power in HVAC Systems,
Types of motors
used in HVAC Systems,
Types of pumps
used in HVAC/refrigeration,
Parts consuming
power as per used unit/system,
Motor Nameplate
for Air Conditioner Motor Applications.


The Common Types Of Motors Used In HVAC Industry
First:
the Common Types of Motors Used in HVAC Industry to drive Compressors
1
SinglePhase Hermetic Motors:
1.1 Split Phase (SP),
1.2 CapacitorStart, InductionRun (CSIR), 1.3 CapacitorStart, CapacitorRun (CSCR), 1.4 Permanent Split Capacitor (PSC),
2
PolyPhase Hermetic Motors.
Second:
the Common Types of Motors Used in HVAC Industry to drive Fans
1 ShadedPole Motors
HVAC System Units And Ratings
Energy Conversions In Air Conditioning /
Refrigeration Systems

HVAC Equipment Power Rating Calculations – Part Two

Difference between Service, Feeder and Branch circuit load
calculation
First: The HVAC System Contribution in
Service/Feeder Load Calculations
First: NEC Standard Method
Second: NEC Optional Calculation Method
First: For Single Dwelling Units
Second: Multifamily Dwelling
Third: Two Family Dwelling (That are Supplied By a Single
Feeder)
Forth: Existing Dwelling Unit


NEC Code & the
Hermetic Refrigerant MotorCompressors
Sizing Calculations for Air Conditioning and
Refrigeration Equipment as Per Article 440:
First: Sizing Calculations for Disconnecting Means:
Case# 1: The load type is a single hermetic motor
only as per 440.12(A),
Case# 2: The load type is a Combination loads as per
440.12(B).

HVAC Equipment Power Rating Calculations – Part Four 
The Minimum Circuit Ampacity (MCA)
Maximum OverCurrent Protection (MOP) or
(MOCP)
Second: Sizing
calculation for BranchCircuit ShortCircuit and GroundFault Protection
Devices
Case# 1: The load type is a single hermetic motor
only as per 440.22(A),
Case# 2: The load type is a Combination loads as per
440.22(B).
Case# 2A: Where a hermetic refrigerant motorcompressor is
the largest load,
Case# 2B: Where a hermetic
refrigerant motorcompressor is not the largest.


Third: Sizing Branch Circuit Conductors Case# 1: The load type is a single hermetic motor only as
per 440.32,
Special Case:
For a WyeStart, DeltaRun Connected MotorCompressor
Case# 2: The load type is a Combination loads as
per 440.33.
Fourth: Sizing Controllers
Case# 1: Controller Serving Motor Compressor only as per 440.41(A), Case# 2: Controller Serving More Than One Load as per 440.41(B). 
HVAC Equipment Power Rating Calculations – Part Six 
Fifth: Branch Circuit Overload Protection
The methods for providing overload protection for the motorcompressors are listed as follows: 1A separate overload relay, 2A thermally protected motorcompressor, 3A fuse or inverse time circuit breaker, 4A special protective system.
Sixth: Provisions for Room Air Conditioners
1 Sizing BranchCircuit ShortCircuit and GroundFault Protection 2 Sizing Branch Circuit Conductors 3 Sizing Disconnecting Means 4 Protection Device for the Cord 

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